Japanese Laid-open Patent Publication No. 2014-034912 (referred to as “JP Publication 912”, hereinafter) discloses a control apparatus for a vehicle that calculates a first vehicle speed based on vehicle wheel speeds, calculates a second vehicle speed based on a rotation speed of an output shaft of a transmission, determines a difference between the calculated first and second vehicle speeds, determines whether vehicle speed information is normal based on the value of the difference, and prevents an automatic stop of an engine when it is determined that the vehicle speed information is not normal.
The configuration disclosed in JP Publication 912 only determines whether the vehicle speed information is normal, but does not determine whether there are any abnormality in the vehicle wheel speed sensors.
Abnormality states of the vehicle wheel speed sensors include a rationality, in addition to a broken wire, a short circuit between a power supply and a ground, an abnormal output state (i.e., Out of Range), etc. The rationality may cause a reduction in reliability of vehicle speed information based on the vehicle wheel speed sensors. Thus, it is useful to precisely detect the rationality.
According to the configuration disclosed in JP Publication 912, if the vehicle speed information is not normal, based on the premise that the second vehicle speed is normal, it can be estimated that there is some abnormality in the vehicle wheel speed sensors used to calculate the first vehicle speed.
Here, under a situation where the vehicle is stuck in a muddy ground, for example, a relatively great drive force due to an accelerator pedal operation by a driver may cause the wheel slip. The wheel slip may cause the difference between the first vehicle speed and the second vehicle speed to be great even if the vehicle wheel speed sensors are normal. Thus, according to a way of merely determining an abnormality of the vehicle wheel speed sensors based on only the difference between the first vehicle speed and the second vehicle speed, there is a problem that a accuracy in detecting the abnormality may be reduced. It is noted that such a problem also occurs even with a way of merely determining an abnormality of the vehicle wheel speed sensors based only on the difference between respective values of the vehicle wheel speed sensors. This is because the wheel slip may cause the difference between the respective values of the vehicle wheel speed sensors to be great even if all the vehicle wheel speed sensors are operating normally.
As a solution to such a problem, there may be a way of determining, only in a vehicle stopped state in which the wheel slip does not occur, whether the respective values of the vehicle wheel speed sensors are within a normal range (i.e., greater than or equal to 0, and less than or equal to a predetermined value) to detect the abnormality of the vehicle wheel speed sensors.
However, it is difficult for such a way to detect the abnormality in such a mode in which the value of the vehicle wheel speed sensor is smaller than its normal value. This is because the vehicle wheel speed sensor having the abnormality in such a mode outputs the value near 0 in the vehicle stopped state, and thus there is probability that the value is regarded as normal.
Therefore, some embodiments provide an abnormality information generating apparatus, etc., that can detect an abnormality of a vehicle wheel speed sensor in a mode in which a value of the vehicle wheel speed sensor becomes smaller than its normal value.